It is known that a silicone rubber powder that contains epoxy groups is used as an agent for improving properties of coatings, organic resin compositions, resins that are used as sealing agents for semiconductor devices, etc. In particular, silicone rubber powders obtained by a condensation reaction have much higher dispersibility in organic resins than similar powders obtained by an addition reaction. Silicone rubber powders obtained by a condensation reaction are known in the art. For example, Japanese Unexamined Patent Application Publications S64-70558, H02-113079 and H08-109262 disclose a silicone rubber powder obtained by curing an aqueously dispersed silicone rubber composition comprising a diorganopolysiloxane capped at both terminals with silanol groups, an organohydrogenpolysiloxane having in one molecule at least two silicon-bonded hydrogen atoms, an epoxy-containing alkoxysilane, and a condensation-reaction catalyst.
However, the aforementioned known silicone rubber powder has an epoxy equivalent that exceeds 3,000 (which means that the amount of epoxy groups introduced into this silicone rubber powder is low). Therefore, such a powder either has insufficient dispersibility in organic resins, or, when incorporated into a curable epoxy resin composition, does not provide sufficient decrease of modulus of elasticity in a product obtained by curing the composition. The inventors herein have undertaken a study aimed at finding reasons for which the epoxy groups cannot be introduced into the silicone rubber powder in a sufficient amount. The study revealed that this occurs because the de-alcoholation reaction that takes place between the silanol groups of the diorganopolysiloxane capped at both molecular terminals with silanol groups and the silicon-bonded alkoxy groups contained in the epoxy-containing alkoxysilane is preceded by a dehydration condensation reaction between the aforementioned silanol groups and the silicon-bonded hydrogen atoms contained in the organohydrogenpolysiloxane.
It is an object of the present invention to provide a silicone rubber powder that has a low epoxy equivalent and possesses excellent dispersibility in organic resins.
It is another object to provide a method for efficient manufacturing of the aforementioned silicone rubber powder.